ES2615388A1 - Procedure and device for the generation of continuous fibers of nanometric diameter, as well as generated nanometric fibers (Machine-translation by Google Translate, not legally binding) - Google Patents

Abstract

Procedure and device for the generation of continuous fibers of nanometric diameter, as well as generated nanometric fibers. The present invention describes a process for the generation of long fibers of nanometric diameter by the combined application of a gas jet and laser radiation. The nanometric fibers generated by said process as well as a suitable device for its implementation are also object of this invention. (Machine-translation by Google Translate, not legally binding)

Description

PROCEDURE AND DEVICE FOR THE GENERATION OF CONTINUOUS NANOMETRIC DIAMETER FIBERS, AS WELL AS GENERATED NANOMETRIC FIBERS

5 FIELD OF THE TECHNIQUE

The present invention is framed within the techniques of processing materials to produce nanomaterials, that is, materials in which at least one of its dimensions has a nanometric scale.

The technique described in the present invention allows to produce continuous fibers and

10 separated whose diameter is in the nanometric scale and its length is indefinitely long.

BACKGROUND OF THE INVENTION

There is a huge demand for new materials with unique properties that allow significant advances in various technological fields. This demand stimulates the synthesis and application of new nanomaterials that meet these new needs. Of the different types of nanomaterials explored, quasi-dimensional materials, such as nanowires and crystalline nanotubes or amorphous nanofibers, are among the most prominent. This is due to its remarkable properties given by an extraordinarily high area ratio

20 superficial with respect to its volume and its reduced diameters. In addition, if nanofibers reach a macroscopic length, they can serve as a valuable bridge between macroscopic applications and nanometric properties, making possible a profitable variety of nanomaterial applications.

However, the synthesis of nanowires or nanofibers of high lengths and their

25 integration into the sustainable production of functional materials continues to present important challenges. There are several industrial methods for obtaining inorganic or polymeric glass fibers with diameters in the micrometer range (microfibers). All of them entail the fusion of the precursor material so that it can be stretched by one of the three fundamental techniques listed below: 1) fibration

Rotary fiberizing, which is based on the centrifugation of the molten precursor through holes made in a drum that rotates at high speed; 2) the

melt blowing, which is based on the extrusion of molten precursor material through a hole, while a jet of gas drags and cools the filament; 3) the methods of mechanical traction, which use different varieties of mechanical systems to induce axial tension in a molten preform that undergoes a uniaxial elongation forming a uniform filament. However, it is not possible to obtain continuous nanofibers of indefinite lengths with any of these methods.

On the other hand, electrospinning or electro-stretching is a scalable technique for the production of nanofibers with high productivity. This is a simple and efficient technique that allows nanofibers to be obtained from a material that must be in a liquid state. Therefore, it has been used to obtain polymer nanofibers. However, the production of ceramic nanofibers is very complex with this method due to its high melting point. Therefore, sol-gel materials must be used as precursors. But the results of this method are not always entirely satisfactory: the calcination of the sol-gel precursor involves certain disadvantages, since nanofibers acquire a high porosity after the process, which gives them poor mechanical properties. In other cases, the fibers are welded to each other during the curing and calcination process, which produces a bonded network that cannot be separated, sorted or knitted. In addition, the incompatibility between some sol-gel precursor chemical compounds restricts the range of compositions of the final product.

Alternatively, the Laser Fiber technique (in English, "Laser Spinning." Patent No. ES2223290B1) is presented as an effective method for producing amorphous ceramic nanofibers. This technique overcomes the limitations of conventional glass fiber production methods, since it allows the production of nanofibers of various compositions including those with a high melting point, also those that generate a fragile melt or have a high tendency to devitrification The nanofibers produced with the “Laser Spinning” technique have a cylindrical morphology, solid and without porosity, separated from each other, so that they can be separated, sorted and knitted. Essentially, the “Laser Spinning” technique consists in the fusion of a small volume of a solid precursor by means of a high-power laser, while a jet of supersonic gas is injected into the fusion zone. This jet of gas drags the molten material causing its extremely rapid elongation and cooling, which produces the amorphous nanofibers with the same composition of the precursor material, in high quantities and in a very short time. However, this technique also has some limitations: the fibers produced do not all have the same diameter, but

They differ from each other. On the other hand, nanofiber lengths are limited to the centimeter range. In addition, the nanofibers obtained are mixed with small drops of molten material that must be extracted before use.

Therefore, there is a need in the state of the art for new procedures that allow the manufacture of solid, continuous and non-porous fibers, of controlled diameter in the nanometric range and with indefinitely long lengths.

BRIEF DESCRIPTION OF THE INVENTION

The present invention provides a process for the production of solid, continuous and non-porous fibers, with controlled diameter in the nanometric range and with indefinitely long lengths. This method is based on the microfusion of a preform of precursor material with a high power laser to generate a microfilament of molten material. At the same time, a jet of gas fed coaxially to the microfilament, with a high speed produces its elongation and cooling.

In a first aspect the present invention provides a suitable process for the production of continuous nanofibers characterized in that it comprises the following steps:

a) provide a preform of elongated shaped precursor material and longitudinally move the preform at a uniform speed towards a processing zone,

b) as the preform of precursor material reaches the processing zone, maintaining the uniform speed, continuously apply laser radiation on the region of the preform that is entering the processing zone to heat to a suitable melt temperature, Y

c) continuously apply gas coaxially to the melt of precursor material and in the same direction of displacement, so that by combined action of the heating produced by laser radiation and the coaxial application of the gas occurs in the processing zone a uniaxial stretching of the melt of precursor material in the direction of displacement, thus reducing its diameter, and

d) as the melt of precursor material of reduced diameter leaves the processing zone, said melt continues to stretch

by the action of the coaxial gas and it cools, solidifying, to form a nanofiber.

The advantage of this procedure over "melt blowing" is that, in the present invention, the processes of heating by the laser beam, as well as the cooling by the gas jet occur much more rapidly than in the "melt blowing". Due to this, the heating can be carried out up to higher temperatures without the rupture of the flow due to instability or capillary forces, since the heating and cooling processes are much faster than the rupture flows. Performing the process at a higher temperature also entails the advantage that the viscosity of the fluid filament will be lower, therefore elongation occurs very quickly and, consequently, the diameter of the material preform can be reduced. precursor in factors less than 1/1000. In this way, nanometric diameters can be achieved without rupture or crystallization of the filament.

Regarding the “Laser Spinning” technique, there are notable differences in the method of implementation, experimental configuration and results. First, in the "Laser Spinning" technique, the precursor material must be in the form of a flat plate and not a cylinder as in the present invention. In the "Laser Spinning" technique, the joint action of the laser beam and the gas stream produces a cut or groove in a solid plate of the precursor material. The laser beam strikes perpendicularly on the flat plate of precursor material and the gas stream strikes obliquely on the plate, forming, in turn, a certain angle with the laser beam. In said method, nanofibers are produced from a small volume of molten material generated in said cut or groove of the plate of precursor material. Sometimes, this implies a low use of the precursor material and a vague control of the nanofiber diameters. On the contrary, in the process of the present invention, one or more laser beams radiate from one or more directions and perpendicularly or slightly obliquely an elongated preform (for example, cylindrical or substantially cylindrical), which is provided with a uniform velocity. . Meanwhile, the gas jet wraps the processing zone flowing in coaxial direction with the molten filament. In this way, the entire volume of the precursor material preform that reaches the processing area is transformed into a nanofiber, so that the use of the precursor material is 100%.

On the other hand, the fibers obtained by the "Laser Spinning" technique are accompanied by small drops of molten material that must be removed before their practical use.

As an example, a cylindrical preform with a circular section of 600 micrometers in diameter and one meter in length could be transformed into a fiber of 300 nanometers in diameter and 4106 meters. In addition, the process of the present invention allows precise control of the diameter of the fibers produced by proper selection of the flow parameters of the precursor material, heating by the laser beam and the coaxial gas jet regime that produces its cooling and elongation. .

As far as the results are concerned, this is the only technique known to date that allows to obtain continuous nanofibers of indefinitely long length of materials with high melting point without using precursors of different chemical nature than the product. In this sense, it has a clear advantage over the electrospinning technique, since in the electrospinning technique materials with a low melting point or chemical precursors in the form of sol-gel should be used. On the contrary, in the method object of the present invention, the fibers are obtained directly from a process that involves the fusion of a precursor material with the same chemical composition as the product, so that the disadvantages derived from curing and calcination do not appear of a sol-gel precursor.

In a second aspect, the invention is directed to the nanofibers obtained according to the defined procedure which have a diameter between 1 and 900 nm and a length between 1 cm and 4x106 m. As indicated above, the nanofibers obtained by the process of the present invention are advantageously solid, continuous and non-porous.

Specifically, the nanofibers obtained by the process of the invention are solid, non-porous and continuous, in addition, there are no restrictions on the chemical composition of the product due to incompatibilities of the precursors. Other advantages of the product obtained with the present invention over electrospinning is that the fibers obtained are completely separated from each other and are long and flexible, so that they can be ordered, aligned and knitted.

In another aspect the present invention provides a device for the production of fibers according to the method of the invention comprising:

a) a processing head comprising:

 means for housing a preform of precursor shaped material

elongate and move it longitudinally at a uniform speed

towards a processing zone, and

 means to apply gas coaxially to the material and in it

direction of travel in and out of the zone of

processing Y

b) a set of optical systems suitable for focusing laser radiation

on the precursor material as it enters the processing zone.

The nanometric fibers obtained by means of the process object of the present invention, can be used for the manufacture of flame retardant fabrics, as reinforcement of polymers for the manufacture of composites, as a support material for different types of cells in tissue engineering, for regeneration. of bones, for the regeneration of mucous membranes, for the regeneration of skin, for the regeneration of cartilage, or the manufacture of bifunctional and recyclable active filters.

DESCRIPTION OF THE DRAWINGS

To complement the description that is being made and in order to help a better understanding of the characteristics of the invention, the following figures are attached as an integral part of said description, where the fundamental elements of the assembly have been schematically represented as an illustration experimental according to different practical examples.

A processing head (2) of a device according to an embodiment of the present invention for the injection of gas (4) coaxially (8) with the flow is shown schematically and in cross-section. of precursor material (1). Two laser beams (6 and 7) are also represented that radiate the preform of the precursor material in the processing zone (3) from opposite directions obtaining a microfilament. The reduction of the preform diameter in the processing area (5) is also shown schematically until a continuous nanometric fiber (9) is produced at the outlet.

In figure 2, the configuration of the optical elements necessary to carry out the experimental assembly of a device according to an embodiment of the present invention is schematically represented in two views corresponding to plan and elevation. In the scheme, two beams of laser radiation (10) and (11) are directed towards two mirrors of total reflection (12) and (13). The propagation of both beams (16) and

(17)

it is modified by means of identical optical instruments (18) and (19) to achieve the desired irradiance on the preform (14). The scheme shows the preform emerging from the processing head (15), and the processing area irradiated by the two beams in opposite directions where the transformation of the preform of the precursor material into a continuous and nanometric fiber (20) occurs.

Figure 3 schematically represents in a plan view an experimental assembly of a device according to an embodiment of the present invention in which the processing zone is irradiated by three identical laser beams (21), (22) and (2. 3). The three beams are directed towards the preform (24) from directions that form an angle of 120 ° to each other in the horizontal plane. Preform

(24)

It is concentric with the processing head (25). The propagation of the three beams (21), (22) and (23) is modified by means of identical optical instruments (26), (27) and (28). The preform of the precursor material is transformed into a continuous and nanometric fiber (29).

Figure 4 schematically represents in a plan view, an experimental assembly of a device according to an embodiment of the present invention in which the processing zone is irradiated by four identical laser beams (30), (31), (32) and (33) that form an angle of 90 ° to each other in the horizontal plane. The laser radiation is directed towards the preform (34) that is concentric to the processing head (35). The propagation of the four beams (30), (31), (32) and (33) is modified by means of identical optical instruments (36), (37), (38) and (39). The preform of the precursor material is transformed into a continuous and nanometric fiber (40).

DETAILED DESCRIPTION OF THE INVENTION.

Process

The present invention provides a suitable process for the production of continuous nanofibers of indefinitely long length characterized in that it comprises the following steps:

a) provide a preform of elongated precursor material and

longitudinally move the preform at a uniform speed towards

a processing zone,

b) as the preform of precursor material reaches the processing zone, maintaining the uniform speed, continuously apply laser radiation on the region of the preform that is entering the processing zone to heat to a suitable melt temperature, Y

c) continuously apply gas coaxially to the melt of precursor material and in the same direction of displacement, so that by combined action of the heating produced by laser radiation and the coaxial application of the gas occurs in the processing zone a uniaxial stretching of the melt of precursor material in the direction of displacement, thus reducing its diameter, and

d) as the melt of precursor material of reduced diameter leaves the processing zone, said melt continues to be stretched by the action of the coaxial gas and cools, solidifying, to form a nanofiber.

The precursor material, in the context of the present invention, is preferably an inorganic glass, a polymer, a ceramic material, a metal or a metal oxide, whose rheological behavior varies with temperature such that, when heated by radiation laser achieves an adequate relationship between its viscosity and its surface tension. In a particular embodiment, the precursor material is selected from the group consisting of silica, phosphate base glass, and polymers such as polylactic acid (PLA) or polycaprolactone (PCL). In a more particular embodiment, the precursor material is silica. The optimum viscosity to favor the stretching of the preform of precursor material to a nanometric fiber depends on the properties of each precursor material. Said optimum viscosity will be sufficiently reduced to allow a rapid flow of uniaxial elongation of the preform as a result of the process gas entrainment. At the same time, the viscosity must be kept high enough so that the surface tension does not cause the filament to break due to the action of the capillary forces.

The precursor material may be in a liquid, semi-solid or solid state. In a preferred embodiment, the precursor material is in a solid or semi-solid state. However, the precursor material can also be provided completely molten, and is then considered a liquid.

The precursor material has an elongated shape. In the context of the present invention, "elongated shape" means the elongated shape in which one dimension is greater than the other two dimensions. Said elongated shape may, for example, have a circular, triangular, elliptical, square, rectangular or any other polygon section. In a particular embodiment, the preform of the precursor material has a substantially cylindrical or substantially rectangular prismatic shape.

In a particular embodiment, the precursor material preform is a cylinder with a circular section having a diameter between approximately 1 μm and approximately 10 mm, preferably between approximately 5 μm and approximately 5 mm, more preferably between approximately 10 μm and approximately 1 mm In a preferred embodiment the diameter of the section is between about 100 µm and about 700 µm, preferably between about 200 µm and about 600 µm, more preferably between about 300 µm and about 600 µm. In a preferred embodiment, the precursor material preform is a cylinder with a circular section having a diameter of approximately 600 µm. In another preferred embodiment, the precursor material is a silica cylinder with a circular section having a diameter of approximately 600 µm.

The preform of precursor material is provided or fed at a uniform speed to the processing zone. In the context of the present invention, "uniform speed" means a speed that remains constant throughout the process. In a particular embodiment the uniform rate at which the preform is provided is between about 0.01 and about 100 µm / s, preferably between about 0.1 and about 50 µm / s, more preferably between about 0.5 and about 10 µm / s. In a preferred embodiment, the uniform rate at which the preform is provided is approximately 1 µm / s.

As the preform of the precursor material reaches the processing zone, maintaining the uniform speed, continuously apply laser radiation on the region of the preform that is entering the processing zone to heat to a suitable melting temperature, obtaining a Micrometric volume melt. In a particular embodiment, the precursor material is melted and / or heated in a micrometer volume comprised between 10 and 900 cubic micrometers, preferably in a micrometer volume comprised between 100 and 800

cubic micrometers, more preferably between 200 and 600 cubic micrometers, even more preferably between 300 and 500 cubic micrometers.

In a particular embodiment, in step b) of the process of the invention a high power laser is used to melt and / or raise the temperature of the precursor material. Preferably, the laser radiation is generated from a selected laser source of Nd: YAG, Nd: glass, Nd: vanadate, Er: YAG, Yb: YAG, Tm: YAG, diode, fiber, disk, CO2, CO, HeCd, of copper, iodine, argon, krypton vapor and chemical lasers (HF, DF). Preferably, the power of the laser source is at least 300 W. In a preferred embodiment the laser equipment used is a CO2 laser ( = 10.6 m) that emits a radiant flow of 950W.

Laser radiation strikes the precursor material from one or more directions so that it is absorbed into the precursor material uniformly with respect to the axis of symmetry of the precursor material. In a particular embodiment, the laser radiation of stage b) comes from two laser beams. Preferably, the two laser beams are identical. In a preferred embodiment the two laser beams are facing each other forming an angle of approximately 180 °. More preferably, the laser radiation of step b) of the process comes from two identical laser beams facing each other forming an angle of approximately 180 °. A processing head for carrying out the process of the invention is shown schematically in FIG. 1 where two laser beams radiate the preform of the precursor material in the processing zone from opposite directions. Likewise, in figure 2 the processing area is shown schematically being irradiated by two beams in opposite directions.

In an alternative embodiment, the laser radiation of stage b) comes from three laser beams. Preferably, the three laser beams are identical. In a preferred embodiment, the three laser beams are at an angle of approximately 120 ° to each other. More preferably, the laser radiation of stage b) comes from three identical laser beams forming an angle of approximately 120 ° to each other. In figure 3 the processing area is schematically represented being irradiated by three identical laser beams.

In an alternative embodiment, the laser radiation of stage b) comes from four laser beams. Preferably, the four laser beams are identical. In a preferred embodiment the four laser beams are at an angle of approximately 90 ° to each other. More preferably, the laser radiation of step b) comes from four identical laser beams forming an angle of approximately 90 ° to each other.

In Figure 4 the processing area is schematically represented being irradiated by four identical laser beams.

The absorption of the laser radiation by the precursor material causes extremely fast fusion of the solid or semi-solid precursor material at a temperature above the melting point or glass transition, or the heating of the precursor material if it is already in a state liquid.

According to step c) of the process of the invention, a gas stream is applied continuously coaxially to the melt of precursor material and in the same direction of movement. The gas stream is coaxially fed at a high speed, which can be supersonic and is typically between about 300 and about 900 m / s, such as about 515 m / s, which is equivalent to 1.5 times the speed of the sound. The combined action of the heating produced by the laser radiation and the coaxial application of the gas produces a uniaxial stretching of the melt of the precursor material in the process zone in the direction of displacement, thus reducing its diameter until obtaining a microfilament of molten precursor material. Additionally, a force can be applied to favor microfilament formation. In the context of the present invention, the force exerted on the precursor material is generally the force of gravity or an external tensile force.

In step d) of the process of the invention, the microfilament of molten material obtained in step c), as it leaves the processing area, continues to be stretched continuously by the action of the coaxial gas that surrounds its entire perimeter. The high velocity gas jet produces rapid elongation and, having left the laser radiation action zone, the molten material cools and forms a solid, continuous, nanometer-sized fiber. The cooling of the fiber obtained is carried out by convection of heat from the gas flow at high speed on the surface of the nanofiber.

In a particular embodiment, the continuous supply of the flow of precursor material to the processing zone, together with the continuous and uniform heating thereof by the laser beam, and the continuous flow of the coaxial gas jet, all of them in the proper ratio, establish a steady state in the process of heating, elongation and cooling. This steady state in the processing zone entails the continuous transformation of the preform of the precursor material

in a fiber of nanometric diameter with an indefinite length, only limited by the duration of the process and its speed.

Nanofibers

In another aspect, the invention is directed to the nanofiber obtained according to the process of the invention. In a particular embodiment, the nanofiber obtained according to the process of the invention has a nanometric diameter, for example a diameter between about 1 and about 900 nm, and an "indefinitely long" length, for example a length between about 1 cm and approximately 4x106 m. According to particular embodiments, the nanofiber obtained according to the process of the invention has a diameter of from about 1, 50 or 100 nm to about 700, 500 or 300 nm. In a particular embodiment, the diameter is approximately 300 nm. According to particular embodiments, the nanofiber obtained according to the process of the invention has a length of from about 1, 100 or 1000 cm to about 5, 10, 100 or 1000 m. Preferably the nanofiber obtained according to the process of the invention has a diameter between about 1 and about 500 nm and a length between about 1 and about 5 m.

Advantageously, the nanofibers obtained by the process of the present invention are solid, continuous and non-porous.

Device

The present invention provides a device for carrying out the process of the invention for the production of continuous fibers. Thus, in a particular aspect the invention relates to the device for the production of fibers according to the process of the invention, which comprises:

a) a processing head comprising:

 means for housing a preform of precursor shaped material

elongate and move it longitudinally at a uniform speed

towards a processing zone, and

 means to apply gas coaxially to the material and in it

direction of travel in and out of the zone of

processing Y

b) a set of optical systems suitable for focusing laser radiation

on the precursor material as it enters the processing zone.

The processing head of the device of the present invention allows the precursor material to be accommodated and moved to the processing area where the laser radiation takes place on the precursor material. In addition, the processing head allows the injection of the process gas coaxially with the flow of precursor material. In a particular embodiment the processing head contains an annular conduit through which the process gas flows coaxially to the microfilament by wrapping it around its perimeter. The high speed gas jet produces a rapid elongation and cooling of the molten material forming a solid, continuous and nanometric-sized fiber.

In a particular embodiment, the device of the invention contains a set of optical systems that focus at least one laser radiation on the precursor material, preferably two laser radiation, more preferably three laser radiation. Preferably, the set of optical systems is formed by mirrors oriented to direct the laser radiation to the processing area.

The laser radiation can come from any laser equipment that generates a radiation with a wavelength suitable for it to be absorbed and transformed into heat in the precursor material and with an emission power large enough to produce heating of the preform throughout the elongation process Depending on the materials to be processed, the appropriate wavelength and operating mode (continuous or pulsed) will be selected. Thus, in a particular embodiment the laser radiation in the device of the invention will be continuous or pulsed.

In a particular embodiment, the laser radiation of the device of the invention is selected from Nd: YAG, Nd: glass, Nd: vanadate, Er: YAG, Yb: YAG, Tm: YAG, diode, fiber, disk, CO2, CO, HeCd, copper vapor, Iodo, Argon, Kripton or chemical lasers (HF, DF).

Figure 1 shows a processing head suitable for the device of the present invention. The precursor material (1) is fed continuously in a

duct inside the processing head (2). The precursor material is supplied in the form of a solid or cast cylinder with a precisely controlled flow rate by means of a feed system not described or shown in the scheme. The processing head guides the preform of the precursor material towards the processing area (3) maintaining its coaxial position aligned with the axis of the head (8) and limiting its oscillations. At the same time, the process gas is injected, from the rear of the processing head, into an annular conduit

(4) coaxial with the conduit of the precursor material and completely enveloping it. Said conduit is designed to carry out the expansion of the gas until a high flow rate is reached that can be supersonic and that forms a jet with low turbulence at the exit of the processing head (5). The process gas flow is designed to wrap the preform in the processing zone producing a very fast drag and cooling effect due to the high friction and heat convection of the high velocity gas flow over the surface of the preform.

In a particular embodiment, in the device of the invention the laser radiation comes from two identical laser beams, more preferably the two identical laser beams are facing each other forming an angle of approximately 180 °. Preferably, the two laser beams (6) and (7) with the same radiant flow and the same irradiance distribution of the laser radiation in their respective cross sections, affect the preform in the processing zone from diametrically opposite directions. Both beams are duly directed on the preform of the precursor material to produce a symmetrical irradiance distribution with respect to the middle plane containing the axis (8) and is transverse to the plane of incidence of both beams. The irradiance distribution of both beams on the preform is adjusted by the set of optical systems of the device of the invention to achieve heating of the preform in the processing zone. Under the combined action of the heating produced by the two laser beams (6) and (7) and the drag produced by the coaxial gas jet (5), the preform undergoes rapid uniaxial elongation in the direction of the axis (8). In this way its diameter is reduced continuously in the processing zone (3) until a continuous nanometric filament (9) is generated. Likewise, the rapid cooling that this filament undergoes as soon as it leaves the area irradiated by the laser beams solidifies the fluid filament forming a dense and continuous nanometric fiber.

An example of assembly of the optical elements necessary to produce an adequate distribution of the irradiance of the laser beams in the processing area to achieve the stability of the process is shown in Figure 2. Two beams of laser radiation

(10)

and (11) with the same wavelength, the same radiant flow and the same transverse distribution of irradiance are directed towards two mirrors of total reflection

(12)

and (13). Said mirrors are used to facilitate the alignment of both beams so that they strike from opposite directions in the preform of the precursor material.

(14)

and symmetrically with respect to its axis. This scheme shows the preform emerging from the processing head (15). The propagation of both beams (16) and (17) is modified by means of identical optical instruments.

(18)

and (19) to ensure that the distribution of irradiance in the processing area is adequate. Both optical instruments consist of a combination of convergent and / or divergent, spherical and / or cylindrical lenses positioned in such a way that the desired irradiance distribution on the preform is achieved (14). The heating generated by the radiation absorption of the laser beams in the precursor material, combined with the friction and cooling caused by the flow of the process gas (not shown in this scheme), results in the transformation of the preform of the precursor material into a continuous and nanometric fiber (20).

In a particular embodiment, in the device of the invention the laser radiation comes from three identical laser beams forming an angle of approximately 120 ° to each other. As an alternative to the previous configuration, Figure 3 schematically depicts in a plan view, an experimental assembly in which the processing area is irradiated by three identical laser beams. Three laser radiation beams (21), (22) and (23) with the same wavelength, the same radiant flux and the same transverse irradiance distribution are directed towards the preform

(24)

from directions that form an angle of 120 ° to each other in the horizontal plane, as shown in the figure. In this way an irradiance distribution is achieved in the cross section of the preform more homogeneous than with the previous configuration of two beams. This scheme shows the concentric preform with the processing head (25). The propagation of the three beams (21), (22) and (23) is modified by means of identical optical instruments (26), (27) and (28) to ensure that the irradiance distribution in the processing area is the right one Said optical instruments are constituted by a combination of convergent and / or divergent, spherical and / or cylindrical lenses positioned in such a way that the desired irradiance distribution on the preform is achieved (24). The heating generated by the radiation absorption of the laser beams in the precursor material, combined with the friction and cooling caused by the flow of the process gas (not shown in this scheme), results in the transformation of the preform of the precursor material into a continuous and nanometric fiber (29).

In another particular embodiment, in the device of the invention the laser radiation comes from four identical laser beams forming an angle of approximately 90 ° to each other. Figure 4 schematically represents in a plan view, another alternative configuration in which the processing area is irradiated by four identical laser beams. Four beams of laser radiation (30), (31), (32) and (33) with the same wavelength, the same radiant flux and the same transverse irradiance distribution are directed towards the preform (34) from directions that form An angle of 90 ° to each other in the horizontal plane, as shown in the figure. In this way an irradiance distribution is achieved in the cross section of the more homogeneous preform than with the previous configurations of two and three beams. This scheme shows the concentric preform with the processing head (35). The propagation of the four beams (30), (31), (32) and (33) is modified by means of identical optical instruments (36), (37), (38) and (39) to make the distribution The irradiance in the processing area is adequate. Said optical instruments are constituted by a combination of convergent and / or divergent, spherical and / or cylindrical lenses positioned in such a way that the desired irradiance distribution on the preform is achieved (34). The heating generated by the radiation absorption of the laser beams in the precursor material, combined with the friction and cooling caused by the flow of the process gas (not shown in this scheme), results in the transformation of the preform of the precursor material into a continuous and nanometric fiber (40).

In a particular embodiment, the device further comprises a source of laser radiation, preferably two sources of laser radiation. More preferably, three or four sources of laser radiation.

As used herein, the term "approximately" means a slight variation of the specified value, preferably within 10 percent of the specified value. However, the term "approximately" may mean a greater tolerance of variation depending for example on the experimental technique used. One skilled in the art understands such variations of a specified value and is within the context of the present invention. In addition, to provide a more concise description, some of the quantitative expressions provided herein are not qualified with the term "approximately." It is understood that, whether the term "approximately" is explicitly used or not, it is intended that all amounts provided herein refer to the given actual value, and are also intended to refer to the approximation to that given value. that would be reasonably deduced based on the usual experience in the

technique, including equivalents and approximations due to experimental and / or measurement conditions for such a given value.

EXAMPLE

Continuous nanofibers of pure silica with length indefinitely have been produced

5 long, whose cross section is cylindrical and uniform diameter of 300 nanometers, at a rate of 4 m / s. The precursor material was a cylindrical preform of pure silica of 600 micrometers in diameter that was fed into the processing zone at a rate of 1 μm / s. A processing head was used with a process gas duct designed to expand until obtaining a

10 supersonic flow of approximately Mach 1.5. The process gas is compressed air supplied at a gauge pressure of 300 kPa. The laser equipment used was a CO2 laser (λ = 10.6 μm) continuously emitting a beam with a radiant flow of 950 W with a Gaussian irradiance distribution. Said beam was divided into two beams of identical radiant flow, 475 W each. Every

The beam was directed towards the processing area by means of two copper mirrors with an angle of 160 ° between them on the side of the precursor material inlet. Before entering the processing area, each beam was transformed by two identical optical instruments, each formed by a spherical lens and a cylindrical lens. Such optical instruments produced a radiation distribution of

20 each beam in an approximately elliptical section of 30 mm and 2 mm axes centered on the processing area, such that the direction of the greater side of said ellipse coincided with the direction of the axis of the preform.

Once the nature of the present invention has been sufficiently described, as well as how to put it into practice, it only remains to add that as a whole and parts that the

It is possible to introduce changes in form, materials and arrangement as long as said alterations do not substantially vary said invention.

Claims (22)

1. Procedure for the production of a continuous nanofiber characterized in that it comprises the following stages: 5 a) provide a preform of elongated shaped precursor material and longitudinally move the preform at a uniform speed towards a processing zone, b) as the preform of precursor material reaches the processing zone, maintaining the uniform speed, apply so 10 laser radiation continues over the region of the preform that is entering the processing zone to heat to a suitable melt temperature, and c) continuously apply gas coaxially to the melt of precursor material and in the same direction of travel, 15 so that by combined action of the heating produced by the laser radiation and the coaxial application of the gas, a uniaxial stretching of the melt of the precursor material in the direction of travel occurs, thus reducing its diameter, and D) as the melt of precursor material of reduced diameter leaves the processing zone, said melt continues to be stretched by the action of the coaxial gas and cools, solidifying, to form a nanofiber. Method according to claim 1, wherein the laser radiation of stage b) comes from two identical laser beams facing each other forming an angle of approximately 180 °. 3. The method according to claim 1, wherein the laser radiation of the 30 stage b) comes from three identical laser beams forming an angle of approximately 120 ° to each other. 4. The method according to claim 1, wherein the laser radiation of the step b) comes from four identical laser beams forming an angle between them of approximately 90 °.

5.

Process according to any of the preceding claims, wherein the precursor material is selected from the group consisting of an inorganic glass, a polymer, a ceramic material, a metal and a metal oxide.

6.

Method according to any of the preceding claims, wherein the laser source used to generate the laser radiation is selected from Nd: YAG, Nd: glass, Nd: vanadate, Er: YAG, Yb: YAG, Tm: YAG, diode, fiber, disk, CO2, CO, HeCd, copper vapor, Iodine, Argon, Kripton or chemical lasers (HF, DF).

7.

Method according to any of the preceding claims, wherein the coaxial gas is applied at a speed between 300 and 900 m / s.

8.

Method according to any one of the preceding claims, wherein the precursor material preform is a silica cylinder with a circular section having a diameter of 600 µm.

9.

Method according to any of the preceding claims, wherein the speed of displacement of the preform towards the processing area is between 0.01 and 100 µm / s.

10.

Nanofiber obtained according to the procedure defined in any one of the preceding claims which has a diameter between 1 and 900 nm, and a length between 1 cm and 4x106 m.

eleven.

Nanofiber according to claim 10, which has a diameter between 1 and 500 nm, and a length between 1 and 5 m.

12.

Device for the production of fibers according to the method defined in claims 1 to 6 comprising: a) a processing head comprising:

 means for accommodating a preform of elongated shaped precursor material and moving it longitudinally at a uniform speed towards a processing zone, and  means for applying gas coaxially to the material and in the same direction of movement in and out of the processing area; Y b) a set of optical systems suitable for focusing laser radiation on the precursor material as it enters the processing zone.

13.

Device according to claim 12 wherein the laser radiation comes from two identical laser beams facing each other forming an angle of approximately 180 °.

14.

Device according to claim 12, wherein the laser radiation comes from three identical laser beams forming an angle of approximately 120 ° to each other.

fifteen.

Device according to claim 12, wherein the laser radiation comes from four identical laser beams forming an angle of approximately 90 ° to each other.

16.

Device according to any of claims 12-15, wherein the laser radiation is generated from a laser source selected from Nd: YAG, Nd: glass, Nd: vanadate, Er: YAG, Yb: YAG, Tm: YAG, diode, fiber , disk, CO2, CO, HeCd, copper vapor, Iodine, Argon, Kripton and chemical lasers (HF, DF).

17.

Use of the nanofiber according to claims 10 and 11 for the manufacture of fire retardant fabrics.

18.

Use of the nanofiber according to claims 10 and 11 as polymer reinforcement for the manufacture of composites.

19.

Use of the nanofiber according to claims 10 and 11 for bone regeneration.

twenty.

Use of the nanofiber according to claims 10 and 11 for the manufacture of bifunctional and recyclable active filters.

21. Use of the nanofiber according to claims 10 and 11 as a support material for different types of cells in tissue engineering. 22. Use of the nanofiber according to claims 10 and 11 for the regeneration of 5 mucous membranes. 23. Use of the nanofiber according to claims 10 and 11 for skin regeneration. 10. Use of the nanofiber according to claims 10 and 11 for cartilage regeneration. Figure 1 Figure 2 Figure 3 Figure 4